PLEASE HELP! ('97 CHEVY )

1997 Chevrolet Malibu

'97 Chevy malibu, 100,000 miles. I have had my car at the mechanic twice in the past two months because the car didn't feel right and the check engine light came on. They gave me a tune up and a Motorvac. The light is off but the car still doesn't feel right. It doesn't feel as powerful, I have some rough idling, and when I drive it just feels rough. It doesn't feel right, I don't know how else to describe it. I'm not great with cars and my mechanic hasn't fixed the prob, so I was wondering if anyone had any ideas. Thanks so much!